Circuit - Box

You select Circuit => Box to open the Box Settings dialog box in order to display the parameters of the circuit box, as well as to allow for modification of those parameter values. The default box size for a new circuit is 160 mils X 160 mils with a cell size of 10 mils X 10 mils.

The entries in this section define the area of the box, and include Cell Size, Box Size and Num. Cells. Changing one of the entries will cause the other settings to be updated. The dialog box allows you to ”lock” any of these values while entering changes. These three values are related in the following manner:

Cell Size: This entry row defines the size of a single cell of the box area. You enter an X dimension (width) and a Y dimension (height). If you wish the cell size to remain constant when changing either of the other size settings, click on the lock check box at the end of the entry row.

Selecting cell size is important. The EM analysis automatically subsections the circuit based on the cell size. Small cells result in slower but more accurate analyses.

Cell Size Calculator: Clicking on this button opens the cell size calculator which allows you to enter your critical circuit dimensions to calculate an optimal cell size which provides the needed level of accuracy while using the minimum processing resources.

Box Size: This entry row defines the size of the box area. You enter an X dimension (width) and a Y dimension (height). If you wish the box size to remain constant when changing either of the other settings, click on the lock check box at the end of the entry row.

Alternatively, if you wish to set the box size and location using the mouse, click on the Set Box Size with Mouse button. Then click in the Project Editor window on the location of one corner of the new box, then drag to the opposite corner. A blue outline appears indicating the new box size and the vertices are identified with open circles and the sides with open squares which identify the handles. You may change the box size by dragging the handles with your mouse.

Num. Cells: This entry row defines the number of cells in the box area. You enter an X dimension (width) and a Y dimension (height. If you wish the number of cells to remain constant when changing either of the other size settings, click on the lock check box at the end of the entry row. You may define the Num. Cells using a variable, see below.

Fields in which you may enter a variable instead of a constant value are identified with a drop down list, an example of which is pictured below. The list includes the entry <Add Variable> in addition to any existing parameters. Selecting <Add Variable> from the list opens the Add/Edit Variable dialog box to allow you to create the variable. If an existing variable is entered, then the entry <Edit Variable> appears in the list. Selecting this entry opens the Add/Edit Variable dialog box to allow you to edit the presently selected variable.

Note that directly typing in the name of a variable which is not yet defined, instead of selecting <Add Variable> from the drop list, also causes the Add/Edit Variable dialog box to appear when this dialog box is closed so that you can define the new variable.

Note that if the cell size is not locked, the project editor picks the closest allowed cell size which allows for an integer number of cells to fit in the box area specified by the Box Size and Num. Cells.

Estimate Memory: Click on this button to get an estimate of the amount of memory needed to analyze the circuit using the present cell and box size. For more information about Estimate Memory, click here.

Symmetry check box: You specify whether symmetry is turned on or off by clicking on the Symmetry check box. Most circuits should have symmetry off. If a circuit is symmetric about the center line parallel to the X axis, then activating symmetry results in a 4X - 8X faster analysis and reduces the memory required to 1/4 to 1/3 of what was needed before symmetry was turned on.

When symmetry is turned on, everything below the line of symmetry is ignored, and all metal above the line of symmetry is ”reflected” about the symmetry line. Therefore, you may enter in just half of your circuit, making sure that you enter in the half that is above the line of symmetry.

Special care should be given to ports when using symmetry. Please refer to the "Ports" chapter in the User's Guide for a detailed explanation of port placement when symmetry is used.

It is recommended that first time users enter the entire circuit when using symmetry, not just half the circuit. This way, toggling symmetry on and off will affect only the speed of the analysis, not the final result.

This option allows you to select the metal type for the box top and box bottom. You can choose either a predefined metal type or user defined metal type. You may not use a metal type that is defined using the thick metal model for a box top or bottom.

WG Load is useful for modeling infinite arrays. The top or bottom cover is terminated with a perfectly matched waveguide load. Note this is not the same as an open environment. To model an open environment select Free Space, which sets the impedance of the cover to 377 ohms/ sq, the impedance of free space. Note that the sidewalls are always modeled as perfect conductors.

Top Metal: Use the drop list to select the metal type for the top of the box. Choose a metal type from the list which includes the default types of WG Load, Free Space, and Lossless in addition to any user defined metal types.

Bottom Metal: Use the drop list to select the metal type for the bottom of the box. The metal types are the same as listed above for the box top.